Fiber optic technology is increasingly being utilized in cellular communications networks for a variety of purposes. Optical fiber generally has increased transmission capacity over copper wire and is generally more resistant to the effects of electromagnetic interference. Whereas this technology is being incorporated into cellular networks, the present state of incorporation does not efficiently utilize the fiber optic cable in the cable topologies of the fiber optic networks. This is particularly so in a fiber optic repeater distributed antenna system network.
FIG. 1 illustrates two base transceiver station (BTS) hubs 110 and 112 of a fiber optic repeater distributed antenna system network 100 which are interconnected by a network backbone 114. Other components of the network are not illustrated since they, and their functionality in the network, are well-known in the art, e.g., mobile switching office (MSO) and the Public Switched Telephone Network (PSTN).
The backbone generally includes optical fibers that may be bundled in a plurality of buffer tubes. These optical fibers are used not only to interconnect the BTS hubs of the network, but additionally, to connect a repeater node 116 to a hub of the network. Repeater node 116 may be an optical repeater that is used in the distributed antenna system (DAS) network. As is known, the DAS node extends the coverage area of a cell. Generally, the remote repeater node 116 is connected to one of the BTS hubs by a fiber(s) that is broken out from the network backbone 114. As can be seen, optical fiber 114A is broken out from the backbone and is utilized to connect node 116 to BTS 110. Whereas only one DAS node 116 is illustrated as being attached to BTS 110, as can be understood, there may be many DAS nodes coupled to BTS 110 and there may be many other DAS nodes coupled to the other BTSs in the network 100. This cable topology shown in FIG. 1, where an optical fiber is broken out from the backbone to couple a DAS node to a BTS presents drawbacks. These drawbacks are particularly compounded when many DAS nodes are coupled to the many BTSs that may be incorporated into the fiber optic repeater distributed antenna system network.
A problem with the topology illustrated in FIG. 1 is that when the optical fiber is broken out from the backbone to couple the node to a BTS hub, the continuously running fiber in the backbone is cut and run from the one BTS hub to the node. Thus, the cut fiber is terminated at the node. This optical fiber run 114A can be seen in FIG. 1. Thus, the optical fiber run 114A from BTS hub 110 to node 116 is an efficient use of this portion of the fiber from the backbone. However, that portion of the fiber in the backbone that is on the other side of the coupled node, i.e., extending in the backbone between node 116 and BTS hub 112, is wasted since the fiber is broken out from the backbone and terminated at node 116 from BTS 110. Thus, this remaining portion of the optical fiber in the backbone is wasted, at least for this physical location of the backbone fiber. This is an inefficient use of the optical fiber in the backbone, and as can be understood, when many DAS nodes are connected to many BTSs in the network in this manner, this inefficiency is multiplied many times over.
An additional drawback with the topology of FIG. 1 is the lack of the ability of the network to recover from an interruption of service between BTS 110 and DAS node 116. As can be seen, the only connection of DAS node 116 to network 100 is through BTS hub 110 and the optical fiber run 114A. As discussed above, the optical fiber that couples BTS hub 110 to DAS node 116 is terminated at the DAS node and the fiber on the other side of the coupled node remains unterminated in the backbone. Thus, as can be understood, if for any reason BTS hub 110 becomes inoperative or the fiber run 114A becomes unable to transmit an optical signal between the BTS hub and the node, network service associated with DAS node 116 will be lost. Therefore, the fiber optic cable topology of FIG. 1 does not provide sufficient redundancy for the fiber optic repeater distributed antenna system network.
Therefore, there is a need for a fiber optic cable topology for a fiber optic repeater distributed antenna system network that provides for greater efficiency for the use of the optical fibers in the cable topology and redundancy in the network.